The present invention relates to an improved valve gasket for a metering valve, and to a fluid dispenser device including a metering valve provided with such an improved valve gasket.
Dispenser device valves are well known in the state of the art. They are mainly used with aerosol receptacles for dispensing fluids charged with propellant (dissolved gas under pressure). When the valve is a metering valve, it generally comprises a valve body enclosing a metering chamber defined axially by two annular gaskets, namely a valve gasket and a chamber gasket, and a valve rod mounted to move between a rest position and an actuating position. The valve rod is urged by a spring into its rest position, in which a shoulder on said rod bears against the bottom surface of said valve gasket. In order to actuate the metering valve, it is necessary to press on the valve rod which slides in the valve body inside the annular gaskets until it reaches its actuating position, in which a metered quantity of fluid is expelled. The spring then returns the valve rod to its rest position. Metering valves of this type are described in Documents EP-0 551 782, EP-0 350 376, FR-2 615 172, FR-2 615 173, and FR-2 615 124.
A problem that arises with the valve rods of valves, in particular of metering valves, concerns in particular leaktightness at the valve gasket. Firstly, it must be possible for the valve rod to slide between its actuating position and its rest position under the effect of the spring, while also preventing leaks from occurring. Secondly, when the valve rod is in the rest position, the leaktightness must be total in spite of the pressure inside the metering chamber and inside the receptacle.
To solve those problems, known valves generally have cylindrical valve rods such that, in alignment with said shoulder, and at least over the portion of the valve rod that slides in the valve gasket, the valve rod has a constant outside diameter that is approximately equal to (in general very slightly greater than) the inside diameter of the central opening in the valve gasket. To guarantee leaktightness in the rest position, a frustoconical portion is generally provided adjacent to said shoulder and extending axially over a portion of the thickness of said valve gasket. Thus, the valve rod slides in the valve gasket with friction, the force exerted by the spring being greater than said friction, and, in its rest position, the frustoconical portion adjacent to said shoulder participates in providing sealing at the valve gasket.
A drawback with such a configuration lies in the fact that the friction that appears while the valve rod is sliding can be relatively high, which can result in said valve rod sticking. In addition, the friction can deform the edge of the valve gasket that is in contact with the valve rod, so that the fluid can penetrate between said rod and said gasket. In particular, when the fluid is in the form of a powder, this can hinder or even prevent metering valve operation.
That phenomenon is further amplified when, in particular for ecological reasons, it is desired to replace propellant gases that are harmful to the environment, such as chlorofluorocarbons (CFCs), with propellant gases that are not harmful to the environment or that are less harmful to the environment, such as, for example hydrofluoroalkane (HFA) gases. Unfortunately, the use of such xe2x80x9cenvironmentally-friendlyxe2x80x9d gases implies a major increase in the pressure inside the valve body, it being possible for such an increase to be as large as 50%. It is therefore necessary to provide even greater leaktightness at the valve gasket, which implies even higher friction between the valve rod and said gasket.
One possible solution to overcome that drawback is to provide a spring having sufficient stiffness. However, that requires a considerable amount of force to be exerted in order to actuate the metering valve, which is undesirable.
Another solution consists in coating the valve rod with a layer of silicone to improve its sliding qualities. That solution is relatively satisfactory with propellant gases such as CFCs, but it is not satisfactory when HFA gases are used. HFA gases expel the silicone during use of the valve, so that after it has been used a certain number of times, the problem of the valve rod sticking reappears.
An object of the invention is to provide a valve gasket for a metering valve that is designed to avoid undesired sticking of the valve rod due to friction between it and the valve gasket, while said valve rod is moving relative to the valve gasket, while also guaranteeing leaktightness at said valve gasket during this movement.
Another object of the invention is to provide a valve gasket that is designed to enable the valve rod to operate reliably and safely with a spring of low stiffness, thereby making it easier to actuate.
Yet another object of the invention is to provide a metering valve that operates with a propellant gas that is not harmful to the environment, said valve including a valve rod that can slide in the valve gasket between its actuating position and its rest position under the effect of the spring without leakage and without any risk of it sticking.
To these ends, the invention provides a valve gasket for a metering valve serving to dispense a fluid in the form of a powder dispersed in a propellant gas, said metering valve comprising a valve body defining a metering chamber, and a valve rod mounted to slide in said metering chamber between a rest position and an actuating position, the sealing between said valve rod and said metering chamber being provided by said valve gasket, said valve body being fixed in a fixing cap serving to assemble the valve onto a fluid reservoir, said valve gasket being provided with a radially inside contact zone over which said valve rod slides, said contact zone being fixed to a rigid element so that, while said valve rod is moving, said contact zone of the valve gasket remains substantially unchanging in terms of its shape and of its position, said contact zone having a profile that is rounded at least in part, so as to reduce the area of contact between said valve gasket and said valve rod, said rigid element being an integral part of said fixing cap, and in particular the inside radial edge thereof. Thus, for given dimensions of the valve rod, said rod slides with lower friction, thereby avoiding sticking of the valve rod, while also guaranteeing excellent leaktightness.
The use of such a valve gasket thus makes it possible to avoid any deformation of the valve gasket, thereby preventing any fluid from being trapped between the rod and the gasket.
Advantageously, said valve gasket is fixed, in particular snap-fastened, to the inside radial edge of said fixing cap.
In a variant, said valve gasket is molded directly over said inside radial edge of said fixing cap.
The present invention also provides a metering valve including such a valve gasket, and it also provides a fluid dispenser device including such a metering valve.